Keywords
hearing loss - unilateral - child - language development - language
Introduction
Since the implementation of the public policy that makes universal newborn hearing
screening (UNHS) compulsory, there has been a higher incidence of early diagnosed
hearing loss. Among the impairment types, unilateral hearing loss (UHL) is commonly
diagnosed in school-age children, at around 5 years of age.[1]
[2] UHL identification in most children occurs initially (38%) through school screening[3] and secondarily through parental suspicion (16%).[2]
UHL is considered a minimal impairment, as well as mild degrees of hearing loss, high-frequency
hearing loss, and conductive hearing loss. However, even the term minimal is controversial, as it might imply that these losses are not important or seem of
little consequence.[4]
Childhood is a critical period for language development and maturation of the central
auditory system. Studies[5]
[6]
[7] have shown that hearing loss, in one single ear, can cause a decline in word recognition.
This phenomenon may be observed in children with moderate bilateral hearing loss who
were monaurally aided and demonstrated a significant decline in word recognition performance
in their unaided ears for at least 4 years.[4] Health care professionals and teachers pay little attention to minimal hearing loss
because they believe it can have very little influence in language and communication
development and in school performance.[8]
[9]
Parents may not notice any hearing problems during the first year of life of their
children who suffer from UHL, due to the superiority of the hearing stimulus reception
in relation to noise. When the child starts crawling and/or walking, this difference
may become evident due to the increasing distance of the sound stimuli and the interference
of background noise.[10] The fitting of a personal amplification devices at this stage could help the early
development of listening skills and minimize any language difficulties that might
occur due to the discrepancy of sound stimuli reception, generating an inadequate
stimulation of the central auditory system[11] and integration of auditory information.
Children with UHL are more likely to experience academic difficulties, have behavioral
problems, be more distracted, have greater need for tutoring,[4]
[12] and show lower performances in oral language compared with their peers with normal
hearing.[2] Yoshinaga-Itano et al[13] concluded that without early identification and intervention, about one third of
the children with mild bilateral or UHL will present difficulties in different areas
of communication.
An important discussion topic is how beneficial the use of hearing aids could be for
children with UHL, because the ear with hearing within normal thresholds can compensate
for the ear with a weaker hearing threshold, creating difficulties only for sound
localization, and in the presence of environmental noise. However, even with this
compensation, children with UHL usually have greater difficulties in understanding
speech.[14] Unlike bilateral hearing loss, there is no consensus of the benefit of the intervention
and use of hearing aids in unilateral congenital conductive hearing loss.[15]
The American Academy of Audiology with its Pediatric Amplification Protocol[16] states that children with mild hearing loss are considered candidates for amplification
and/or use of individual frequency modulation (FM) systems. The decision of amplification
in children with UHL is made by the family based on individual needs as well as audiological,
developmental, communicative, and educational factors.[10]
Bilateral hearing loss, even fluctuating or mild, is enough to impair listening skills[17] and has implications in language development. This occurs as a consequence of inadequate
reception of sound stimuli, causing the child's central auditory system to receive
inconsistent stimulation, which hinders the perception of environmental sounds.[11]
In UHL, speech difficulties are not yet a consensus, because studies[18]
[19] have shown that children with this type of hearing loss reorganize their auditory
cortex and may present similar development as their peers with normal hearing. Another
bibliographical survey[11] on the impact of otitis media in children's language pointed out that even those
children with mild UHL may present compromised language acquisition.
The objective of this study was to determine, based on a survey of national and international
recently published articles, which language disorders may occur in children with UHL
and what types of tests were used to identify such disorders.
Methods
To perform the bibliographical survey, researchers previously defined the criteria
for the inclusion and exclusion of national and international articles and the bibliographical
research period. This systematic review of the UHL literature used the following inclusion
criteria: articles should study samples of children, aged between 3 months and 12
years, with UHL without any other impairment, and articles should include results
of language tests applied to evaluate language disorders in this population. Journal
articles were excluded if the participants had any cognitive or intellectual language
deficits associated with UHL. Articles that reported only the incidence of UHL unrelated
to language development were also excluded from the study.
A bibliographical survey of scientific articles published over the past 10 years was
performed (between the years of 2001 and 2011) using three different databases: PubMed
(www.pubmed.gov), Lilacs, and the Cochrane Library (regional.bvsalud.org). To ensure that there were
no publications on the same subject, we began searching in the Cochrane Library, and
no studies addressing similar subjects were found.
The descriptors (DeCS/MeSH) used for searches in the databases were: (1) hearing loss,
unilateral; (2) language; (3) child; (4) preschool; (5) vocabulary test; (6) language
test; (7) language development; (8) child language; (9) language comprehension; (10)
language comprehension test. In all databases, searches were performed using descriptors
in English and using the simple search.
Twelve strategies were used three databases. Each strategy was a combination of three
descriptors (DeCS/MeSH), separated manually by the operator AND. The 12 strategies
obeyed the descriptors combination as follows: 1, 2, 3 (strategy 1); 1, 2, 4 (strategy
2); 1, 5, 3 (strategy 3); 1, 5, 4 (strategy 4); 1, 6, 4 (strategy 5); 1, 7, 3 (strategy
6); 1, 7, 4 (strategy 7); 1, 6, 3 (strategy 8); 1, 8, 6 (strategy 9); 1, 9, 3 (strategy
10); 1, 8, 5 (strategy 11); and 1, 8, 10 (strategy 12).
Initially, the selection was made by reading the title and abstract of each study
found in the databases. All the articles that did not meet the inclusion criteria
of this study, that were shown repeatedly in the same or another database, or that
were not available in full by the databases of the university were excluded.
Review of Literature
The researchers collected 236 articles, out of which 226 studies were found in PubMed
(95.8%) and 10 articles in Cochrane (4.2%). No study with the descriptors used was
found in Lilacs.
The numbers of studies found in the three databases are shown in [Table 1], according to the 12 combinations of descriptors (DeCS/MeSH) described as data search
strategies in the Methods section.
Table 1
Number of articles found in each strategy in the different databases
|
Strategy
|
PubMed
|
Lilacs
|
Cochrane
|
|
1
|
37
|
0
|
3
|
|
2
|
24
|
0
|
0
|
|
3
|
17
|
0
|
0
|
|
4
|
17
|
0
|
0
|
|
5
|
14
|
0
|
0
|
|
6
|
26
|
0
|
3
|
|
7
|
17
|
0
|
0
|
|
8
|
20
|
0
|
2
|
|
9
|
20
|
0
|
2
|
|
10
|
1
|
0
|
0
|
|
11
|
17
|
0
|
0
|
|
12
|
16
|
0
|
0
|
|
Total
|
226
|
0
|
10
|
Note: Strategy 1 retrieved largest number of articles, totaling 37 articles containing
the terms “hearing loss,” “unilateral,” “language,” and “child,” followed by strategy
6, totaling 26 articles containing the terms ”hearing loss,” “unilateral,” “language
development,” and “child.”
The initial selection was made by reading the titles and abstracts. At this stage,
all the articles that did not meet the inclusion criteria, articles that referred
only to the unilateral adaptation of hearing aids or cochlear implants in children
with bilateral hearing loss, or articles that used other tests unrelated to language
assessment were excluded. Initially 14 studies were selected for the study.
Three systematic reviews were found, as well as one editorial and four articles that
reported the incidence of UHL without associating it with language development, and
another one in which magnetic resonance imaging was performed to verify the area of
the brain activated through auditory stimulation. They were all excluded from the
study. In the end, only five articles met the inclusion criteria, as shown in [Table 2].
Table 2
Year of publication, authors, and country in which the study was performed, according
to the analysis of selected articles
|
Study
|
Year
|
Authors
|
Country
|
|
1[10]
|
2010
|
Lieu JEC, Tye-Murray N, Karzon RK, Piccirillo JF
|
USA
|
|
2[20]
|
2009
|
Martínez-Cruz CF, Poblano A, Conde-Reyes MP
|
Mexico
|
|
3[18]
|
2007
|
Priwin C, Jönsson R, Magnusson L, Hultcrantz M, Granström G
|
Sweden
|
|
4[21]
|
2003
|
Paradise JL et al
|
USA
|
|
5[22]
|
2002
|
Borg et al
|
Sweden
|
[Table 3] characterizes the participants in the studies of the selected articles, reporting
the total sample size, and how many children had UHL. It also describes the type and
degree of hearing loss only in children with UHL.
Table 3
Number of participants in the studies and type and degree of hearing loss, according
to the analysis of selected articles
|
Study
|
Total sample size/children with UHL
|
Type of loss in children with UHL
|
Degree of loss in children with UHL
|
|
1[10]
|
148/74
|
NR
|
4 children with mild HL; 15 children with moderate HL; 11 children with severe HL;
44 children with profound HL
|
|
2[20]
|
81/21
|
Sensorineural
|
Severe and profound
|
|
3[18]
|
57/8
|
Conductive
|
NR
|
|
4[21]
|
429/NR
|
Conductive
|
Mild and moderate
|
|
5[22]
|
286/55
|
Conductive or sensorineural
|
NR
|
Abbreviations: HL, hearing loss; NR, not reported.
The samples of studies 1 and 2 ([Table 2]) were composed of groups of children with UHL, and these were compared with the
group of children with normal hearing. However, study 5 comprised 55 children with
UHL, 87 with normal hearing, and 144 with bilateral hearing loss. Study 4 compares
the language test results in children with unilateral and bilateral conductive hearing
loss, but did not specify the number of children with UHL. Only in study 3, the sample
was composed exclusively of children with UHL.
Regarding the devices used by the children, study 1 revealed that 22 children used
an FM system, 4 of them used individual hearing aids, 3 used a contralateral routing
of signals, and 3 others used a bone-anchored hearing aid (BAHA). Study 3 showed that
4 participants used a BAHA, but did not mention if they were children or adults. Study
4 used the ventilation tube as an intervention in children under 3 years of age. In
study 5, the children used personal hearing aids, but it did not mention how many
of them used amplification devices. Study 2 did not report the use of devices among
its participants.
[Table 4] shows the tests used for language assessment and other tests used to complement
that same assessment of the children studied.
Table 4
Tests used for language assessment and cognitive aspects, according to the analysis
of selected articles
|
Study
|
Receptive language
|
Expressive language
|
Others
|
|
1[10]
|
Scale listening comprehension
|
Scale oral expression
|
Wechsler Abbreviated Scale of Intelligence
|
|
2[20]
|
Verbal reasoning[4]
|
Verbal reasoning[4]
|
Abstract visual reasoning[a]; numeric reasoning[a]; short-term memory[a]
|
|
3[18]
|
NR
|
NR
|
Swedish phonemically balanced; Swedish phonemically balanced words in noise
|
|
4[21]
|
Peabody Picture Vocabulary Test: Revised
|
Number of different words; spontaneous speech sample; mean length of utterance in
morphemes; percentage of consonants correct: revised
|
McCarthy Scales of Children's Abilities, including general cognitive index; verbal,
perceptual performance, and quantitative subscales;
|
|
5[22]
|
NR
|
Speech motor function; phoneme mobilization; phonology
|
Speech in noise; phoneme discrimination; emotional prosody; language memory; mental
development
|
Abbreviation: NR, not reported.
a Subtests from Stanford-Binet Intelligence Scale of the Terman and Merrill (4th edition,
short version).
It can be observed that out of the 12 tests mentioned in the surveyed articles, which
were done for language assessment, 9 of them were directed toward expressive language
(75%) and 3 (25%) assessed receptive language. Studies 1, 2, and 4 assessed both receptive
and expressive language mastery. None of the tests were repeated in more than one
study. Other tests were conducted to complement language assessment, such as cognitive
and discrimination tests, as well as a test for auditory processing disorders.
By evaluating the results of the language tests used in each study, it is possible
to observe that in study 1 children with hearing loss had a lower performance on both
tests that assessed receptive and expressive languages when compared with children
without hearing loss, but no difference was found in relation to the cognitive aspects.
In study 2, children with UHL have shown lower intelligence quotient (IQ) test scores
when compared with their peers with normal hearing, even when both groups got results
within normal limits.
In study 5, in the overall score, children with UHL showed better scores on the expressive
language tests when compared with children with bilateral hearing loss. However, the
results were lower when the children with UHL were compared with children with normal
hearing. Among the group of children with UHL, those who had sensorineural hearing
loss presented better scores on the tests that assessed expressive language as well
as other auditory skills, when compared with children with conductive UHL.
In study 4, children with UHL achieved better scores on the cognitive tests than those
with bilateral hearing loss. On the receptive language test, children with continuous
UHL achieved lower scores compared with children with bilateral hearing loss (continuous
or intermittent). Regarding expressive language, the group with UHL achieved lower
scores on the vocabulary test compared with the children with bilateral hearing loss.
Even with lower scores, there was no statistically significant difference between
the groups with unilateral and bilateral hearing loss.
With regard to studies conducted exclusively with children with UHL, study 3 showed
that the normal ear tested for speech perception in silence and with background noise
achieved scores close to 100%, which is considered normal. The ear that presented
hearing problems, however, showed scores that were lower than expected.
Discussion
Since 1980, studies have raised questions related to UHL and its implications on people's
lives.[3]
[4] According to the present study, no consensus was found on the impact on language
acquisition and development in children with UHL.
It has been observed, through a bibliographical survey, that few studies have focused
on possible language disorders and, when the issue was approached, it was because
this population was part of heterogeneous groups, which also showed bilateral hearing
loss, among other problems.
Among the studies that have specifically evaluated the language of children with UHL,
a great variety of tests were observed, which demonstrates that there is no standardization
for the evaluation of children with this type of hearing loss.
According to the articles included in this study, it was verified that the tests used
to evaluate language did not meet the protocol requirements for the evaluation of
this skill in children with UHL, but rather they were designed to evaluate children
with other types of language disorders.
It is possible to observe that there was no standardization of language tests for
populations of children with either unilateral or bilateral hearing loss. Moreover,
the scores obtained by children with UHL have been compared with the tests' standardization,
that is, the comparison was performed with a sample of children without language disorders
in relation to age. However, the difficulties presented by children with UHL should
go through qualitative evaluations, because the results of the selected studies[10]
[11]
[18]
[20]
[21] evidenced that there were impacts on difficulties in their language, but they did
not report in which formal and nonformal language levels (phonetic, phonological,
syntactic, semantic, or pragmatic) such difficulties were present.
Concerning the application of the tests, it was found that children with UHL demonstrated
lower scores on both receptive and expressive language tests when compared with their
peers with normal hearing.[10]
[20] When the performance of children with minimal hearing loss was checked,[22] those with UHL obtained better scores on the expressive language tests than the
children with mild bilateral degrees of hearing loss, high-frequency hearing loss,
or conductive hearing loss. Only in one study[21] did the children with UHL achieve lower scores than the ones with mild or moderate
bilateral hearing loss on the receptive and expressive language tests. However, the
differences were not significant between the two groups.
In the cognitive tests, it was observed that children with UHL had similar scores
as children with normal hearing.[10]
[20] When compared with the group of children with minimal hearing loss, children with
UHL achieved better scores.[21]
[22]
Another study[23] reported that vocabulary development in children involves learning meanings and
names of the different objects common to their daily lives, which requires an integration
of perceptual information. It can be assumed that if there is a need for integration
of perceptual information for proper language acquisition and development, even minimal
hearing loss can interfere with this process.
Not all children with UHL will develop learning or communication disabilities, but
early identification of hearing loss is a factor that will contribute to greater attention
to the follow-up of language development and, later on, the school performance of
these children. The use of hearing aids, FM systems, and preferential classroom seating
can help these children improve their school performance. However, this measure alone
might not be able to counter learning disabilities or even assure whether the problems
created in childhood may persist into adulthood.[4]
With regard to the characterization of hearing loss, five of the surveyed studies[10]
[18]
[20]
[21]
[22] indicated the type of hearing loss, and three[10]
[20]
[21] indicated the degree of hearing loss. Concerning the use of hearing aid devices,
four studies[10]
[18]
[21]
[22] revealed their use, however, one[18] did not specify whether they were used in children. These data demonstrate a large
bias in their interpretation, because the participants were not evenly divided, mainly
according to the degree of hearing loss and intervention used, as more severe hearing
loss with late intervention might demonstrate greater impairment in the ability to
identify the acoustic characteristics of speech sounds[24] causing a negative impact on language development. The studies[10]
[18]
[21]
[22] did not report the effectiveness of these devices—in other words, the time of daily
use and the situations in which they were used.
In the articles analyzed,[18]
[22] the main difficulties that children with UHL presented were sound localization and
speech recognition in background noise. The speech recognition skill showed discrepancies
not only in background noise but also in silence, as demonstrated in one of the studies.[22] Concerning sound localization difficulties, if it is present in children with UHL,
it can make the child waste more time trying to locate the speaker in the environment,
thus having reduced attentional and visual cues, and may miss some of the intended
communicative messages.[2]
In a comparative study[25] with 25 children with UHL and their peers with normal hearing, it was concluded
that children with UHL achieved lower scores in sound localization tasks when compared
with normal-hearing children and that such problems increased proportionally to the
hearing loss severity. Speech recognition was also compromised in these children,
both in silence and in noise, regardless of the ear in which the stimulus and noise
were addressed.
Final Comments
There are still many questions about UHL, probably because this type of hearing loss
causes little damage to those who have it, compared with bilateral hearing loss. It
is possible that impairments in other nonauditory functions will arise due to this
loss and consequently interfere with the quality of life of this population.
Few studies were found using language tests in children with UHL or describing language
disorders that occur as a result. Further prospective studies associating language
disorders in children with UHL will be required to establish which language difficulties
can be seen in children with UHL.
Parameters have not been established for the impact on the development of language
in children with UHL, and it is expected that longitudinal studies with standardized
tests are conducted on large samples of children to highlight the consequences of
this type of sensory deprivation in the language.
